This invention relates generally to a filter, and more specifically to a filter employing a liquid-solid contacting chamber and including a unique barrier downstream of a filter bed of particulate solids employed to treat liquid directed through the chamber.
It is common practice in liquid treatment filter systems, such as systems employed in the treatment of water and waste water, to employ a filter bed of particulate solids to remove undesired contaminants from the liquid being treated. Generally the particulate solids making up the filter bed are quite small, e.g., having an average particle size of 0.5 mm or less, requiring the use of one or more inert supporting layers to prevent the filter media from being carried out of the filter system with the liquid being treated. One common approach to supporting such a bed of particulate solids is to provide multiple layers of larger inert particulate material, such as gravel, as the supporting substrate.
One of the benefits of employing one or more gravel supporting layers is that the gravel particles are free to move relative to each other. Therefore, the particles will displace relative to each other as needed to permit particulate contaminants to be trapped in said layer(s). In addition, the relative movement among the gravel particles is of assistance in permitting backwashing liquid to move through the supporting layers and into the filter media with the required velocity to provide the desired cleansing of the filter bed.
However, since the gravel particles are not constrained against relative movement, excessive and uncontrolled shifting of such particles has been known to occur, particularly during backwashing. This excessive and uncontrolled shifting of gravel particles causes "bed upset", resulting in an undesired channeling of liquid through the filter bed. When this occurs it is often necessary to shut down the filter, remove the filter media and the supporting gravel layer(s), and thereafter recharge the system. In addition to increasing the material costs, by requiring the use of additional gravel to form the supporting layer(s) and additional particulate solids to form the filter bed, the "downtime" encountered while the filter is being recharged also is extremely undesirable.
In other filter systems strainers have been employed to both receive the liquid to be treated, after the liquid has passed through a particulate filter bed, and to assist in distributing liquid during the backwashing operation. These strainers commonly have been employed as part of a header-lateral system, such as is disclosed in U.S. Pat. No. 3,826,375, issued to Fournier, or have been mounted directly into a bottom wall of the filter. Although strainers have been employed in filter systems which do not utilize one or more layers of inert materials, such as gravel, to support a filter media bed, such strainers do have certain drawbacks. One of the most common problems experienced in using strainers is that the particulate solids of the filter media (and sometimes the solid contaminants required to be removed from the liquid being treated) tend to clog the strainer openings. When this occurs undesirably high pressure losses across the filter are created, thereby slowing down the filtering operation. Moreover, during backwashing the clogged strainers prevent the uniform distribution of backwashing liquid, thereby preventing the uniform cleansing of the particulate filter bed.
In view of the problems encountered with the above described prior art systems, and in an effort to either eliminate the use of relative expensive gravel supporting layer(s), or at least minimize the amount of gravel employed in such supporting layer(s), Applicants have invented unique barriers. These barriers are positioned downstream of a particulate solids filter bed, as determined by the direction of fluid flow through the filter during the filtering operation, and have elements thereof capable of simulating the desired movement of gravel particles in gravel supporting layers, while eliminating the possibility of excessive movement of the type resulting in bed upset and the undesired channeling of liquids during the filtering and backwashing operations.